1. Field of the Invention
The present invention relates to a groove machining apparatus that forms grooves for oil passages in insulating spacers of oil-filled transformers and a groove machining method for such groove machining apparatuses.
2. Description of the Related Art
Generally, coils of oil-filled transformers are produced by winding a copper wire on which thin insulating paper of several tens of microns is wound into the coil form. Moreover, insulators composed of an insulating plate formed by cutting pressboard having a thickness of several millimeters corresponding to the coil into a predetermined shape and multiple insulating spacers attached to set positions on the insulating plate are arranged between coils and between the coils and ground (see FIG. 8 in JP 8-51036A, for example). Specifically, although insulating spacers are cut into various shapes in accordance with the positions at which the insulating spacers are arranged with respect to the coils, principally, insulating spacers are formed into the shape of a parallelogram whose two non-parallel sides form an angle of 45 degrees, and even though the vertical and horizontal dimensions are slightly different depending on the size or the type of transformers, for example, in the case of a 275 kV transformer used for electric power transmission from a power plant, 50,000 to 60,000 insulating spacers per phase are used.
Here, insulating spacers function as electrical insulation and also function as an oil flow duct that secures a passage for an appropriate insulating oil on the coil surface for the purpose of cooling. In this case, in order to supply the insulating oil to the coil surface more efficiently, formation of grooves in insulating spacers has also been proposed and implemented (see JP 2003-62718A, for example). Specifically, when a short side of an insulating spacer is regarded as the base, a groove parallel to the base is formed, and this groove has a preset width and depth. The center of this groove in a width direction is set to be the middle point of the insulating spacer having a parallelogram shape.
It should be noted that pressboard is a flat plate material that is produced by laminating wet paper made of kraft pulp fiber or the like and applying pressure to the laminate.